The present invention generally relates to fluid flow sensors and more specifically to gas flow sensors for detecting the flow of gas through a conduit, and is especially beneficial in a high pressure gaseous fuel injection system.
The natural gas transmission industry uses a large number of large bore, 2-stroke and 4-stroke cycle, and gaseous fuel engines for compressing natural gas. For example, such engines are used to pressurize and to transport natural gas through the extensive network of natural gas pipelines that supply residential housing and commercial businesses. The network of natural gas pipelines typically operates at high pressure in the neighborhood of between 500 and 1000 psig.
These large bore, natural gas engines may be powered by a small portion of the natural gas passing through the pipelines. Normally, before being injected into the engine, the gas pressure is significantly reduced. Gaseous fuel is typically injected into the engine cylinders by mechanically actuated fuel injectors at pressures typically below about 60 psig. The high level of exhaust emissions and poor fuel economy of these engines, operating with this classical low-pressure fuel gas, has recently become an environmental and economic issue.
It has recently been demonstrated that not only improved exhaust emissions and improved fuel economy, but also improved engine performance can be achieved by injecting gaseous fuel at much higher pressures of about 500 psig (typically between 300 psig. and 1000 psig.). Subsequently, high-pressure fuel injection systems have been developed and are being installed on these large bore engines. The newly developed high-pressure fuel injection (HPFI) systems are electronically controlled, offering the opportunity to optimize fuel injection timing, fuel-air charge mixing, and the resulting combustion process. The injected high-pressure gas induces beneficial fuel-air charge mixing, resulting in efficient combustion.
The use of such high fuel gas pressures, while shown to be very beneficial to combustion quality, introduces a serious new concern. The concern is that if a high-pressure injection valve (HPIV) should fail in the open (gas flowing) condition, a very large quantity of gas will be injected into the engine cylinder in a short period of time. The result of such an occurrence could be serious engine damage, or other potentially hazardous conditions. The failure of an HPIV to close each engine cycle as intended can be caused by numerous possible events involving mechanical, hydraulic, and electronic components in the HPIV system. As a result, the safe and reliable operation of the HPFI system requires that effective safeguards be employed to reduce the quantity of gas injected in the event of a HPIV xe2x80x9cfail openxe2x80x9d event. Reliable and appropriate sensor feed back does not currently exist for such a system.
Another problem associated with the sensing HPIV failure is the difficulty in achieving adequate sensing device cyclic life. A practical application of sensing devices requires that such devices exhibit an operational life of at least 10,000 hours (about 180 million cycles), preferably 20,000 hours (about 360 million cycles) or more, of continuous operation without failure or the need for replacement. Even more desirable, are devices that not only exhibit this long uninterrupted service life, but which can be easily and inexpensively repaired.
It is an objective of the present invention to provide a novel flow sensor that is accurate, highly reliable, fast, and easily adaptable to a wide variety or sizes of fluid systems.
According to one aspect of the present invention, it is an objective of the present invention to provide a mechanism for indicating the proper opening and closing of high-pressure injection valves (HPIVs) in a high-pressure fuel injection system.
In accordance with these and other objectives, the present invention is directed toward a novel flow sensor that includes a spring biased piston responsive to a pressure differential or pressure drop across a selectively sized restriction orifice. The flow sensor includes a valve body assembly having an internal chamber, an inlet passage for connection to the high-pressure source and an outlet passage for connection to the high pressure fuel injection valve or other downstream plumbing orifice. The piston is disposed in the internal chamber for movement that may be sensed. A position sensor in sensory communication with the piston has an output indicating the position of the piston relative to the body assembly. The restriction orifice is arranged between the inlet passage and outlet passage and divides the internal chamber into an inlet pressure region acting on a first end portion of the piston and an outlet pressure region acting on a second end portion of the piston. The piston is biased to one position (preferably by a spring or possibly other such means such a fluid pressure or gravity for example) such that a pressure drop, caused by flow exiting the outlet chamber, is adapted to overpower the force of the bias to move the piston toward a second position.
Other objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.